I am planning a clinical study and need to determine the needed sample size. My primary endpoint will be measured in blood pressure (mmHg). Many studies already exist for this, but they do not often provide sdev for the measurements of blood pressure in hypertensive patients. I did, find a study in Germany (DEGS) that provided the mean blood pressure for treated hypertension and I based my sample size estimation on this. Specifically, I used the values from Treated hypertension in Table 3 Total, namely 130.3 mmHg (129.2 - 131.4) with a n of 7095*0.154 (see DEGS Table 2 Total lower row)
Following the approach described here, I then used
to arrive at a sdev of 18.55125 mmHg.
My question is now: did I do this right? Thank you all for your guidance!